Propylene random copolymers have excellent physical properties and thus, they are used in a wide range of applications. For example, propylene random copolymers are widely used for packaging films; however, there are some cases in the packaging film applications where low temperature heat sealability is required. In order to improve the low temperature heat sealability, the melting point of the propylene random copolymers needs to be lowered. JP-A No. 2-173015 proposes a propylene random copolymer prepared from an aluminoxane and a hafnium compound whose ligand is a polydentate coordination compound in which two groups selected from an indenyl group, a substituted indenyl group and partially hydrogenated form thereof are bonded via a lower alkylene group. Even though the propylene random copolymer described in the publication certainly has a low melting point, the copolymer also has a problem that the anti-blocking property of a film obtained from the copolymer is poor due to the large amount of low-crystalline and low molecular weight fractions.
JP-A No. 9-110934 discloses a propylene random copolymer obtained from a chiral metallocene compound and an aluminoxane. According to the method described in the publication, a propylene random copolymer having a low melting point can be prepared, but there is a problem that atactic polymers are produced as side products in the presence of achiral mesomeric metallocenes that are produced as side products upon the production of chiral metallocene compounds. Therefore, there is a problem that a film obtained from the copolymer has the deteriorated anti-blocking property or the deteriorated haze after heat treatment.
JP-W No. 8-504457 proposes a low melting point propylene homopolymer having a smaller amount of the xylene-soluble fraction. However, since the polymer is a propylene homopolymer, a film obtained therefrom has poor impact resistance.